According to Vandy and Wakefield,[1] as the gastrocnemius and soleus muscles of the calf contract, the pressure in the DVS increases and helps pump the blood towards the heart. The authors[1] also explain that when blood exits the DVS, there is a drop in the pressure of the deep veins, thus allowing blood to passively flow from the superficial venous system through the perforating veins to the DVS. When the muscles of the calf contract again, the circulation of blood from the legs to the heart begins again. As blood flows through the venous systems of the legs back to the heart, 1-way bicuspid valves that are located in the deep veins, the perforating veins, and the superficial veins promote the unidirectional flow of blood and prevent backflow.[1,5]